2. Some clues to LMC star-formation history
Our knowledge of LMC star formation, has, until now, been limited to data from broad-band photometry, mostly of sparsely populated fields. Due to image crowding, mainly relatively bright stars have been reached. Still, it has been clear that different parts of the LMC show different population characteristics. Effects of sporadic bursts of star formation and a stellar population a few Gyears old have been observed (Butcher 1977, Frogel and Blanco 1983, Stryker 1984, Hardy et al. 1984, Bertelli et al. 1992, Vallenari et al. 1996a, b, Gallagher et al. 1996).
Outside the Bar, two populations are mixed (Ardeberg et al. 1985), one old "halo population" and one younger "disk population". Also, LMC clusters show two populations. Older globular clusters are similar to Galaxy counterparts (Searle et al. 1980), while a younger population of clusters has a median age somewhat above 1 Gyear with some clusters up to 4 Gyears old (Flower 1984, Chiosi et al. 1988, Da Costa 1991, Vallenari et al. 1992, Girardi et al. 1995). M giant stars in a field in the Western part of the Bar seem to divide into a smaller young and a larger old population (Frogel and Blanco 1990).
In number and integrated mass, LMC stars of the youngest generations are of smaller importance. Stars defining global galactic properties are much older and may have a chemical composition considerably different from that of the youngest populations. How much older the dominating stars may be, and how different their chemical compositions are, has remained unknown. Of key significance in this respect is the composition of the Bar. Before the current study, little has been known concerning the properties of the bulk population of this dominating LMC structure.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998